This proposal describes a research effort centered on the initial folate-requiring enzyme in the de novo purine biosynthetic pathway, 5,10-methenyltetrahydrofolate: 2-amino-N-ribosylacetamide-5'-phosphate transformylase, isolated from a tumor cell line. Exeriments will be conducted to elucidate possible differences between the enzyme from neoplastic and normal tissue; and the design and synthesis of substrate analogs as potential active-site-directed irreversible inhibitors of the transformylase. All aspects of this work may prove useful in the design of specific transformylase inhibitors for use in the treatment of neoplastic disease through the induction of "purine-less death" as a mechanism of cytotoxicity, as well as furnishing active-site titrants for the transformylase.